In a two channel, full-duplex voice communication system, strong acoustic coupling between the transmit point and the receive point of a channel may lead to echoes occurring in the conservation. Acoustic echo cancellation (AEC) signal processing technology may be used to remove these echoes.
AEC signal processing may rely on accurate alignment between the speaker and microphone streams. Depending on the specific device or driver in use, if the reported delay between speaker and microphone streams is less than the physical delay, the AEC may compensate with only minor loss in echo cancelation quality by buffering the speaker values for cancelation. However, if the reported delay is more than the physical delay, the AEC may be unable to function due to a lack of causality. Severe misalignment, such as beyond a few tens of milliseconds, may have an adverse impact on other echo control modules, such as voice switching or microphone fading. Therefore, echo-free communication, for full or half duplex communication, may rely on alignment within twenty milliseconds of the physical delay between the speaker and microphone streams.
Cross correlation may be used to determine alignment, but cross correlation may suffer from some major drawbacks. Searching over a large number of possible delay values to determine the physical delay may lead to a high computational complexity. Also, the inevitable presence of glitches in a system may break the correlation calculations.